1. Field of the Invention
The present invention relates to a frequency switching circuit that wirelessly transmits information to a receiving apparatus, a transmitting apparatus, a body-insertable apparatus, and a transmitting and receiving system.
2. Description of the Related Art
Conventionally, a capsule body-insertable apparatus wirelessly transmits information, which is acquired in-vivo by, for example, capturing images (hereinafter, in-vivo information), to a receiving apparatus that is carried by a subject. The receiving apparatus continuously waits for transmission of in-vivo information from the body-insertable apparatus. Each time upon receiving the in-vivo information, the receiving apparatus stores the received in-vivo information in, for example, a portable recording medium or transmits the in-vivo information almost in real time to a display device that is connected to the receiving apparatus via, for example, a network cable.
When information is wirelessly transmitted from the body-insertable apparatus to the receiving apparatus, the information to be transmitted is modulated at a predetermined frequency. In order to transmit information stably, it is necessary to obtain a stable modulated frequency. For example, Japanese Laid-open Patent Publication No. 09-107242 discloses, as a transmitting circuit for obtaining characteristics of stable modulated frequency, an FM modulation circuit including a first resistor that sets a modulation signal to a predetermined level and then inputs the modulation signal to an anode of a variable capacitance diode to control a center frequency; and a second resistor that applies a fixed bias voltage to a cathode of a modulation variable capacitance diode.